Vehicular fuel tank filler pipes are currently provided at their upper end with a seal door structure through which the fuel dispenser nozzle must be inserted to introduce fuel into the fuel tank. A known seal door structure comprises a partition having an opening of a diameter sized to admit the fuel dispenser nozzle, and a closure in the form of a flap which is normally spring-biased to close the opening in the partition, but which is displaced to the open position by the insertion of the dispenser nozzle.
It is desirable to use a vaportight seal door in the filler pipe to prevent the venting of fuel vapor to the upper end of the filler pipe and subsequently to the atmosphere when the cap is removed.
It is also known to equip vehicular fuel systems with pressure relief means to relieve excess tank pressure by venting it to the atmosphere. Such pressure relief structure can be mounted in the filler pipe cap, as disclosed for example in U.S. Pat. No. 4,457,325. Pressure relief is sometimes made redundant as shown in U.S. Pat. No. 4,816,045, in which a bypass safety valve vents excess fuel tank pressure around a seal door to the inlet region of the filler pipe, and a cap-mounted relief valve provides additional venting if the pressure relief provided by the bypass safety valve is not sufficient.
A disadvantage with such redundant pressure relief structure is that it requires complicated, space-consuming bypass structure in the filler neck in addition to the seal door itself. Moreover, the seal door of U.S. Pat. No. 4,816,045 requires a bleed orifice and therefore is not vaportight.
Pressure relief filler pipe caps accordingly cannot function where a vaportight seal door closes off the filler pipe; i.e., they are made superfluous by the non-venting seal door. Despite any advantages, then, of the cap-mounted pressure relief concept as primary or secondary tank pressure relief, the prior art has not adequately addressed the need for a simple, compact vaportight seal door assembly with which such caps can be used.
Another disadvantage of prior art vaportight seal doors is that the soft seal material mounted on the door itself or on the partition on which the door seats is often subject to contact with the fuel dispenser nozzle when the nozzle is inserted. This contact abrades or wears the seal material and results in a short seal life.